Android:使用Parcel将对象从一个活动传递到另一个活动时遇到困难

时间:2011-10-25 18:54:03

标签: android android-activity android-intent parcelable parcel

我已经阅读了很多关于如何使用Parcel的文章,我已经在我的应用程序中使用过它,但它无效。我刚刚创建了一个活动,您可以使用Sockets连接到计算机。我在Socket的java.io.PrintWriter上打开了一个OutputStream,我希望有另一个活动(在第一个活动中触摸按钮时打开)使用同样的PrintWriter。我认为我在这里犯的错误是没有克隆PrintWriter object。我不知道如何克隆它。

这是第一个活动(我删除了一些不需要的功能):

public class TestActivity extends Activity implements OnClickListener
{
    String ip;
    int port;
    Socket soc;
    PrintWriter writer;   // this works fine here

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        ip = "";
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // Connect button click handler (you can skip this part)
        Button connect = (Button)findViewById(R.id.connectBTN);
        connect.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                EditText TB = (EditText)findViewById(R.id.ipTB);
                ip = TB.getText().toString();
                TB = (EditText)findViewById(R.id.portTB);
                port = Integer.parseInt(TB.getText().toString());
                try {
                soc = new Socket(ip,port);
                showDialog("Connected successfully!");
                writer = new PrintWriter(soc.getOutputStream(), true);
                }
                catch(Exception er)
                {
                    showDialog("Couldn't connect.\n"+er.getMessage());
                    soc = null;
                }
            }
        } );

        findViewById(R.id.controlmouseBTN).setOnClickListener(this);

        // disconnect click handler  (skip this part too)
        Button disconnectBTN = (Button)findViewById(R.id.disconnectBTN);
        disconnectBTN.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                try
                {
                    if(soc.isConnected()) soc.close();
                    writer.close();
                }
                catch(Exception er) { showDialog("Couldn't close connection.\n"+er.getMessage()); }
            }
        });

    }

    @Override
    public void onClick(View v)   // here is the erroneous part 
    {
        //if(soc == null || !soc.isConnected()) { showDialog("Not connected to any computer."); return; } 
        //if(writer == null) return;
        Intent i = new Intent(getApplicationContext(), PCController.class);
        Intermediate inter = new Intermediate();   // this is the Parcelable class I've created
        //inter.set(new String("hello"));  (I tried sending a string, which worked fine, just to confirm that my Parcelable class is working)
        inter.set(writer);
        i.putExtra("printer", inter);
        startActivity(i);
    }

}

以下是Parcelable类Intermediate的代码

import android.os.*;

public class Intermediate implements Parcelable
{
    Object ob;

    public Intermediate()
    {}

    public Intermediate(Parcel parcel)
    {
        this.ob = parcel.readValue(Intermediate.class.getClassLoader());
    }

    public void set(Object o)
    { this.ob = o; }

    public Object get()
    {
        return ob;
    }

    @Override
    public int describeContents()
    { return 0; }

    @Override
    public void writeToParcel(Parcel dest, int flags)
    {
        dest.writeValue(this.ob);
    }

   // I don't understand this part though! Just copy pasted and modified the ClassName

    public static final Intermediate.Creator<Intermediate> CREATOR = new Intermediate.Creator<Intermediate>() {
        public Intermediate createFromParcel(Parcel in) {
            return new Intermediate(in); }

        public Intermediate[] newArray(int size) {
            return new Intermediate[size]; }
    };  
}

这是被激活的下一个活动的代码。 (我只发布了必要部分)

PrintWriter writer;
    String s;   // for testing purpose
    Swipe swipe;   // a SurfaceView

    public void onCreate(Bundle bundle)
    {
        super.onCreate(bundle);
        swipe = new Swipe(this);
        swipe.setOnTouchListener(this);
        setContentView(swipe);
        Intent i = getIntent();
        Intermediate ob = (Intermediate)i.getParcelableExtra("printer");
        writer = (PrintWriter)ob.get();
        //s = (String)ob.get();
        //showDialog(s);   // this shows up the string I had sent, which means the string is getting passed.
    }

现在当我没有连接(即writer为空)并且我开始下一个Activity时,没有任何反应(没有错误)。 但是当我连接(writer不为空)并且我开始下一个活动时,MAIN活动就会崩溃。我没有费心去记录错误信息,因为我知道我在这里做错了。

任何帮助将不胜感激!谢谢!

编辑:这是异常堆栈跟踪

10-26 00:37:55.445: WARN/System.err(251): java.lang.RuntimeException: Parcel: unable to marshal value java.io.PrintWriter@44eb0b40
10-26 00:37:55.474: WARN/System.err(251):     at android.os.Parcel.writeValue(Parcel.java:1087)
10-26 00:37:55.484: WARN/System.err(251):     at android.test.Intermediate.writeToParcel(Intermediate.java:33)
10-26 00:37:55.484: WARN/System.err(251):     at android.os.Parcel.writeParcelable(Parcel.java:1106)
10-26 00:37:55.494: WARN/System.err(251):     at android.os.Parcel.writeValue(Parcel.java:1029)
10-26 00:37:55.504: WARN/System.err(251):     at android.os.Parcel.writeMapInternal(Parcel.java:469)
10-26 00:37:55.514: WARN/System.err(251):     at android.os.Bundle.writeToParcel(Bundle.java:1445)
10-26 00:37:55.524: WARN/System.err(251):     at android.os.Parcel.writeBundle(Parcel.java:483)
10-26 00:37:55.534: WARN/System.err(251):     at android.content.Intent.writeToParcel(Intent.java:5237)
10-26 00:37:55.544: WARN/System.err(251):     at android.app.ActivityManagerProxy.startActivity(ActivityManagerNative.java:1204)
10-26 00:37:55.554: WARN/System.err(251):     at android.app.Instrumentation.execStartActivity(Instrumentation.java:1373)
10-26 00:37:55.564: WARN/System.err(251):     at android.app.Activity.startActivityForResult(Activity.java:2749)
10-26 00:37:55.574: WARN/System.err(251):     at android.app.Activity.startActivity(Activity.java:2855)
10-26 00:37:55.584: WARN/System.err(251):     at android.test.TestActivity.onClick(TestActivity.java:80)
10-26 00:37:55.594: WARN/System.err(251):     at android.view.View.performClick(View.java:2364)
10-26 00:37:55.606: WARN/System.err(251):     at android.view.View.onTouchEvent(View.java:4179)
10-26 00:37:55.615: WARN/System.err(251):     at android.widget.TextView.onTouchEvent(TextView.java:6541)
10-26 00:37:55.624: WARN/System.err(251):     at android.view.View.dispatchTouchEvent(View.java:3709)
10-26 00:37:55.634: WARN/System.err(251):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
10-26 00:37:55.634: WARN/System.err(251):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
10-26 00:37:55.644: WARN/System.err(251):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
10-26 00:37:55.656: WARN/System.err(251):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
10-26 00:37:55.664: WARN/System.err(251):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1659)
10-26 00:37:55.674: WARN/System.err(251):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107)
10-26 00:37:55.684: WARN/System.err(251):     at android.app.Activity.dispatchTouchEvent(Activity.java:2061)
10-26 00:37:55.694: WARN/System.err(251):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1643)
10-26 00:37:55.705: WARN/System.err(251):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1691)
10-26 00:37:55.714: WARN/System.err(251):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-26 00:37:55.724: WARN/System.err(251):     at android.os.Looper.loop(Looper.java:123)
10-26 00:37:55.734: WARN/System.err(251):     at android.app.ActivityThread.main(ActivityThread.java:4363)
10-26 00:37:55.744: WARN/System.err(251):     at java.lang.reflect.Method.invokeNative(Native Method)
10-26 00:37:55.754: WARN/System.err(251):     at java.lang.reflect.Method.invoke(Method.java:521)
10-26 00:37:55.764: WARN/System.err(251):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
10-26 00:37:55.774: WARN/System.err(251):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
10-26 00:37:55.785: WARN/System.err(251):     at dalvik.system.NativeStart.main(Native Method)
10-26 00:38:02.424: WARN/System.err(251): java.lang.RuntimeException: Parcel: unable to marshal value java.io.PrintWriter@44eb0b40
10-26 00:38:02.454: WARN/System.err(251):     at android.os.Parcel.writeValue(Parcel.java:1087)
10-26 00:38:02.454: WARN/System.err(251):     at android.test.Intermediate.writeToParcel(Intermediate.java:33)
10-26 00:38:02.464: WARN/System.err(251):     at android.os.Parcel.writeParcelable(Parcel.java:1106)
10-26 00:38:02.474: WARN/System.err(251):     at android.os.Parcel.writeValue(Parcel.java:1029)
10-26 00:38:02.486: WARN/System.err(251):     at android.os.Parcel.writeMapInternal(Parcel.java:469)
10-26 00:38:02.494: WARN/System.err(251):     at android.os.Bundle.writeToParcel(Bundle.java:1445)
10-26 00:38:02.505: WARN/System.err(251):     at android.os.Parcel.writeBundle(Parcel.java:483)
10-26 00:38:02.514: WARN/System.err(251):     at android.content.Intent.writeToParcel(Intent.java:5237)
10-26 00:38:02.524: WARN/System.err(251):     at android.app.ActivityManagerProxy.startActivity(ActivityManagerNative.java:1204)
10-26 00:38:02.534: WARN/System.err(251):     at android.app.Instrumentation.execStartActivity(Instrumentation.java:1373)
10-26 00:38:02.544: WARN/System.err(251):     at android.app.Activity.startActivityForResult(Activity.java:2749)
10-26 00:38:02.554: WARN/System.err(251):     at android.app.Activity.startActivity(Activity.java:2855)
10-26 00:38:02.554: WARN/System.err(251):     at android.test.TestActivity.onClick(TestActivity.java:80)
10-26 00:38:02.564: WARN/System.err(251):     at android.view.View.performClick(View.java:2364)
10-26 00:38:02.574: WARN/System.err(251):     at android.view.View.onTouchEvent(View.java:4179)
10-26 00:38:02.584: WARN/System.err(251):     at android.widget.TextView.onTouchEvent(TextView.java:6541)
10-26 00:38:02.594: WARN/System.err(251):     at android.view.View.dispatchTouchEvent(View.java:3709)
10-26 00:38:02.604: WARN/System.err(251):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
10-26 00:38:02.614: WARN/System.err(251):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
10-26 00:38:02.625: WARN/System.err(251):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
10-26 00:38:02.634: WARN/System.err(251):     at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:884)
10-26 00:38:02.644: WARN/System.err(251):     at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1659)
10-26 00:38:02.654: WARN/System.err(251):     at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1107)
10-26 00:38:02.664: WARN/System.err(251):     at android.app.Activity.dispatchTouchEvent(Activity.java:2061)
10-26 00:38:02.674: WARN/System.err(251):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1643)
10-26 00:38:02.684: WARN/System.err(251):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1691)
10-26 00:38:02.694: WARN/System.err(251):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-26 00:38:02.704: WARN/System.err(251):     at android.os.Looper.loop(Looper.java:123)
10-26 00:38:02.714: WARN/System.err(251):     at android.app.ActivityThread.main(ActivityThread.java:4363)
10-26 00:38:02.714: WARN/System.err(251):     at java.lang.reflect.Method.invokeNative(Native Method)
10-26 00:38:02.724: WARN/System.err(251):     at java.lang.reflect.Method.invoke(Method.java:521)
10-26 00:38:02.734: WARN/System.err(251):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
10-26 00:38:02.744: WARN/System.err(251):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
10-26 00:38:02.754: WARN/System.err(251):     at dalvik.system.NativeStart.main(Native Method)

2 个答案:

答案 0 :(得分:3)

你在这里遇到了更大的问题。你不应该使用Parcels在活动之间传递东西。根据android文档:

  

Parcel不是通用序列化机制。此类(以及用于将任意对象放入包中的相应Parcelable API)被设计为高性能IPC传输。因此,将任何Parcel数据放入持久存储中是不合适的:Parcel中任何数据的底层实现的更改都可能导致旧数据不可读。

您应该使用捆绑包。我通常做的是在类中创建两个静态方法,我试图在名为toBundle和fromBundle的活动之间传递。 toBundle接受我想要传输的类的实例并返回一个包。 fromBunle接受一个包并返回该类的实例。

我不知道在Activities之间传递像PrintWriter这样的复杂对象的方法。但是你的代码也存在其他问题。你在主UI线程上做网络的东西。这将导致您的应用程序冻结很多。您需要将所有IO移至另一个线程。这很好,因为那样你就可以将所有IO内容移动到一个可以从两个活动中访问的单独类中。例如,使用IntentService。这将使你的应用程序sooooooo更好。您可能还想阅读文章Painless Threading。这是我推荐给所有Android开发人员的关键读物。

答案 1 :(得分:0)

您无法使用任何常规Android数据传递方法(Bundles / Parcels)在两个Android活动之间传递PrintWriter。如果必须在两个活动之间共享PrintWriter,则可以使用静态变量。

话虽这么说,您也可以编写一个您在每个Activity上访问和使用的服务。您可能需要查看ApiDemos项目中的LocalService示例,以获取有关如何执行此操作的示例。关于这一点,网上也有无数的教程。